The design and performance of gear pumps with particular reference to marginal suction condition
In this thesis an investigation for the identification, measurement and modelling of the gear pump performance under marginal suction condition, created in the suction line and resulting in cavitation at the suction port and cavitation erosion on the delivery side plate is introduced. A new technique for the detection of cavitation in gear pumps has been employed and proved to be more efficient and less expensive than other techniques available. The experimental study has been carried out by monitoring the pressure ripple at the pump inlet and outlet, as well as investigating the pressure distribution around the gear rotor under cavitating and non-cavitating conditions. It was found that the gear pump cavitation appeared in three distinct stages, these being cavitation-inception, discrete-cavitation and continuous-cavitation. These stages of cavit tion were investigated by means of pressure distribution around the gear rotor using a miniature pressure transducer positioned at a gear fillet. The experimental results demonstrate a drop in filling efficiency, of the tooth space due to cavitation, which provides a further understanding of the pump performance characteristics at different inlet conditions. An expression for the definition of transient pressure in the tooth space due to trapped volume has been derived for the first time and proved to give a good correlation with published experimental work. A surface analysis technique has been employed in this work to study the behaviour of the material erosion due to cavitation bubble collapse, using a 'Talysurf 41 instrumentation system, and the results obtained are in good agreement with those published by NEL.